This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of the type which utilizes non-coil springs. Box spring assemblies of this general type have been known since 1964, the first such spring assembly being disclosed in U.S. Pat. No. 3,286,281. Subsequently issued patents disclosing the same general type of box spring assembly are: U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 4,060,862; 4,120,058; 4,131,961; 4,195,376; 4,218,790; 4,238,861; 4,251,892; 4,253,208; 4,339,834; 4,470,584; and 4,739,977.
Box spring assemblies of the general type shown in the above list of patents, all of which are owned by the assignee of this application, are advantageous with respect to the conventional box spring assemblies using coil springs because they provide a desired stiffer foundation for the mattress and contain a reduced amount of wire. These box spring assemblies are also advantageous from the standpoint of prolonged service life, ease of assembly, and cost of manufacture.
Additional box spring assemblies of this general type are shown in U.S. Pat. Nos. 3,546,723; 3,596,299; 3,722,013; 3,825,960; 3,833,948; 3,835,485; 3,869,740; 3,990,121; and 4,000,531.
The principal objects of this invention are to provide an improved spring for box spring assemblies which has limited deflection characteristics to avoid overstressing of the spring during loading, reduce points of stress concentration, and imparts a "flotation" feel to the box spring assembly user which is desirable from a comfort standpoint.
The spring according to the present invention has a load bearing portion at the upper end of an upright yieldable portion. The upright yieldable portion comprises a pair of downwardly extending and converging connecting bars integral at their upper ends with the load bearing portion, a pair of lower torsion bars at the lower end of the connecting bars, and a pair of downwardly extending and converging wire columns located at their upper ends outwardly of the lower torsion bars. Connecting wire sections join the lower torsion bars with the upper ends of the columns. The wire columns are spaced inwardly of the load bearing portion at the upper end of the spring to reduce the likelihood of metal-to-metal contact during deflection with an undesirable "clicking" noise.
As a downwardly directed load is applied to the load bearing portion, the upright columns move toward each other and inward thus causing the upright columns to approach a vertical orientation. When the upright columns reach a substantially vertical orientation, full deflection is reached. The connecting wire sections joining the lower torsion bars with the columns are vertically aligned with spaces in the mattress support deck in between the metal members which form the deck. Thus the clicking sound associated with springs meeting deck members is avoided.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates and from the subsequent description of the preferred embodiment and the appended claims taken in conjunction with the accompanying drawing.